ABO EBAM, Nigeria — In the gloomy shade deep in Africa’s rain forest, the noontime silence was pierced by the whine of a far-off chain saw. It was the sound of destruction, echoed from wood to wood, continent to continent, in the tropical belt that circles the globe.From Brazil to central Africa to once-lush islands in Asia’s archipelagos, human encroachment is shrinking the world’s rain forests.

The alarm was sounded decades ago by environmentalists - and was little heeded. The picture, meanwhile, has changed: Africa is now a leader in destructiveness. The numbers have changed: U.N. specialists estimate 60 acres of tropical forest are felled worldwide every minute, up from 50 a generation back. And the fears have changed.

Experts still warn of extinction of animal and plant life, of the loss of forest peoples’ livelihoods, of soil erosion and other damage. But scientists today worry urgently about something else: the fateful feedback link of trees and climate.

Global warming is expected to dry up and kill off vast tracts of rain forest, and dying forests will feed global warming.

“If we lose forests, we lose the fight against climate change,” declared more than 300 scientists, conservation groups, religious leaders and others in an appeal for action at December’s climate conference in Bali, Indonesia.

The burning or rotting of trees that comes with deforestation - at the hands of ranchers, farmers, timbermen - sends more heat-trapping carbon dioxide into the atmosphere than all the world’s planes, trains, trucks and automobiles. Forest destruction accounts for about 20 percent of manmade emissions, second only to burning of fossil fuels for electricity and heat. Conversely, healthy forests absorb carbon dioxide and store carbon.

“The stakes are so dire that if we don’t start turning this around in the next 10 years, the extinction crisis and the climate crisis will begin to spiral out of control,” said Roman Paul Czebiniak, a forest expert with Greenpeace International. “It’s a very big deal.”

The December U.N. session in Bali may have been a turning point, endorsing negotiations in which nations may fashion the first global financial plan for compensating developing countries for preserving their forests.

The latest data from the Food and Agriculture Organization (FAO) helped spur delegates to action.

“Deforestation continues at an alarming rate of about 13 million hectares (32 million acres) a year,” the U.N. body said in its latest “State of the World’s Forests” report.

Because northern forests remain essentially stable, that means 50,000 square miles of tropical forest are being cleared every 12 months - equivalent to one Mississippi or more than half a Britain. The lumber and fuelwood removed in the tropics alone would fill more than 1,000 Empire State Buildings, FAO figures show.

Although South America loses slightly more acreage than Africa, the rate of loss is higher here - almost 1 percent of African forests gone each year. In 2000-2005, the continent lost 10 million acres a year, including big chunks of forest in Sudan, Zambia and Tanzania, up from 9 million a decade earlier, the FAO reports.

Across the tropics the causes can be starkly different.

The Amazon and other South American forests are usually burned for cattle grazing or industrial-scale soybean farming. In Indonesia and elsewhere in southeast Asia, island forests are being cut or burned to make way for giant plantations of palm, whose oil is used in food processing, cosmetics and other products.

In Africa, by contrast, it’s individuals hacking out plots for small-scale farming.

Here in Nigeria’s southeastern Cross Rivers State, home to one of the largest remaining tropical forests in Africa, people from surrounding villages of huts and cement-block homes go to the forest each day to work their pineapple and cocoa farms. They see no other way of earning money to feed their families.

“The developed countries want us to keep the forests, since the air we breathe is for all of us, rich countries and poor countries,” said Ogar Assam Effa, 54, a tree plantation director and member of the state conservation board.

“But we breathe the air, and our bellies are empty. Can air give you protein? Can air give you carbohydrates?” he asked. “It would be easy to convince people to stop clearing the forest if there was an alternative.”

The state, which long ago banned industrial logging, is trying to offer alternatives.

Working with communities like Abo Ebam, near Nigeria’s border with Cameroon, the Cross Rivers government seeks to help would-be farmers learn other trades, such as beekeeping or raising fist-sized land snails, a regional delicacy.

The state also has imposed a new licensing system. Anyone who wants to cut down one of the forest’s massive, valuable mahogany trees or other hardwoods must obtain a license and negotiate which tree to fell with the nearby community, which shares in the income. The logs can’t be taken away whole, but must be cut into planks in the forest, by people like David Anfor.

He’s a 35-year-old father of one who earns the equivalent of 75 U.S. cents per board he cuts with a whizzing chain saw. “The forest is our natural resource. We’re trying to conserve,” he said. “But I’m also working for my daily eating.”

A community benefiting from such small-scale forestry is likely to keep out those engaged in illegal, uncontrolled logging. But enforcement is difficult in a state with about 3,500 square miles of pristine rain forest - and few forest rangers.

On one recent day deep in the forest, where the luxuriant green canopy allows only rare shards of sunlight to reach the floor, the trilling of a hornbill bird and the distant chain saw were the only sounds heard. As forestry officials rushed to investigate, the saw operator fled deeper into the forest, sign of an illegal operation.

Environmentalists say such a conservation approach may work for rural, agrarian people in Nigeria, which lost an estimated 15 million acres between 1990 and 2005, or about one-third of its entire forest area, and has one of the world’s highest deforestation rates - more than 3 percent per year.

But lessons learned in one place aren’t necessarily applicable elsewhere, they say. A global strategy is needed, mobilizing all rain-forest governments.

That’s the goal of the post-Bali talks, looking for ways to integrate forest preservation into the world’s emerging “carbon trading” system. A government earning carbon credits for “avoided deforestation” could then sell them to a European power plant, for example, to meet its emission-reduction quota.

“These forests are the greatest global public utility,” Britain’s conservationist Prince Charles said in the lead-up to Bali. “As a matter of urgency we have to find ways to make them more valuable alive than dead.”

Observed the World Wildlife Fund’s Duncan Pollard, “Suddenly you have the whole world looking at deforestation.”

But in many ways rain forests are still a world of unknowns, a place with more scientific questions than answers.

How much carbon dioxide are forests absorbing? How much carbon is stored there? How might the death of the Amazon forest affect the climate in, say, the American Midwest? Hundreds of researchers are putting in thousands of hours of work to try to answer such questions before it is too late.